Effect of reduction temperature on the preparation of zero-valent iron aerogels for trichloroethylene dechlorination

Abstract

Zero-valent iron (ZVI) aerogels have been synthesized by sol-gel method and supercritical CO2 drying, followed by H-2 reduction in the temperature range of 350-500 degrees C. When applied to trichloroethylene (TCE) dechlorination, the ZVI aerogel reduced at 370 degrees C showed the highest performance in the conditions employed in this study. Thus, the effect of reduction temperature in preparing ZVI aerogels has been investigated by several characterizations such as BET, XRD, TPR, and TEM analyses. As the reduction temperature decreased from 500 to 350 degrees C, the BET surface area of the resulting aerogels increased from 6 to 30 m(2)/g, whereas their Fe-0 content decreased tip to 64%. It was also found that H-2 reduction at low temperatures such as 350 and 370 degrees C leads to the formation of ZVI aerogel particles consisting of both Fe-0 and FeOx in the particle cores with a different amount ratio, where FeOx is a mixture of maghemite and magnetite. It is, therefore, suggested that reduction at 370 degrees C for ZVI aerogel preparation yielded particles homogeneously composed of Fe-0 and FeOx, in the amount ratio of 87/13, resulting in high TCE dechlorination rate. On the other hand, when Pd- and Ni-ZVI aerogels were prepared via cogellation and then applied for TCE dechlorination, we also observed a similar effect of reduction temperature. However, the reduction at 350 or 370 degrees C produced Pd- or Ni-ZVI aerogel particles in which Fe-0 and Fe3O4 co-exist homogeneously. Since both Fe-0 and Fe3O4 are advantageous in TCE dechlorination, the activities of Pd- and Ni-ZVI aerogels reduced at 350 degrees C were comparable to those of both aerogels reduced at 370 degrees C, although the former aerogels have less Fe-0 content.